Fast-rotating machine parts in transmissions or in motors are usually lubricated with an oil mist which is generated by nozzles. In order to avoid oil loss it is necessary to seal the transmission or motor housing hermetically from the external environment. In the vicinity of shaft feedthroughs, difficulties can arise if radial shaft sealing rings with a sealing lip of an elastomeric material are employed. The extremely thin film of lubrication produced during the operation of such seals, although continuously renewed, can reduce the frictional heat produced only to a limited extent.
DE-OS No. 24 27 537 discloses a seal for the gap between a revolving shaft and the bore of a housing, which includes an outer ring secured to the wall of the housing bore, and an inner ring secured to the shaft. The seal is equipped with a gap seal having return-transport ribs on the side facing the oil stream. A ring-shaped sealing lip is secured to the inner ring which, when the shaft is standing still, is biased against a radially-inwardly directed projection of the outer ring.
When the shaft is at rest, oil may penetrate through the gap seal to the vicinity of the sealing lip. However, the rotation of the shaft creates a dynamically generated back transport of oil from the vicinity of the sealing lip, through the return-transport ribs of the gap seal. Thus, as the shaft begins to rotate, the sealing zone proper increasingly shifts from the sealing lip to the gap seal. Eventually the centrifugal forces resultant from the rapid rotation of the shaft lift the sealing lip completely from contact with the outer ring. At this point the gap seal alone is responsible for the seal. With a still further increase of the speed of the shaft, oil may be essentially emptied out of the sealing gap and, undesirably, ambient air is admitted into the sealing space. This interrupts the further circulation of lubricating oil into the sealing gap. At high speeds, a heat buildup in the residual lubricating oil may result in undesirable secondary phenomena, and in the decomposition of adjacent portions of elastomeric materials.
The technical basis for the function of the seal discussed above requires a particularly high degree of precision manufacturing of every individual part of the seal, and in particular precise mutual fits under operating conditions. The requirement of high precision manufacturing results in extremely high manufacturing costs. Further, the requirement of precise mutual fit cannot be met if the shaft to be sealed runs eccentrically due to operating conditions, for example, as a result of unavoidable vibrations during shaft rotation.